USACO sec2.1 Hamming Codes

直接枚举就行了，不带回溯的搜索。

/*

PROG : hamming

LANG : C++

*/

# include <stdio.h>



# define id(x) ((x)>>3)

# define of(x) ((x)&0x7)

# define get(x) ((h[id(x)]>>of(x))&0x1)

# define set(x) (h[id(x)] |= (0x1<<of(x)))



int n, b, d;

char h[(1<<5) + 1];

int sol[70];

/*************************************************/

int dis(int x, int y)

{

    int s = x ^ y, r = 0;

    while (s)

    {

        ++r;

        s &= s-1;

    }

    return r;

}



void search(int cur, int cnt)

{

    int i, j;

    if (cnt > n) return ;

    for (i = cur+1; i < (1<<b); ++i) if (!get(i))

    {

        for (j = 1; j <= cnt; ++j)

            if (dis(sol[j], i) < d) break;

        set(i);

        if (j > cnt) {sol[cnt+1] = i; search(i, cnt+1);}

    }

}

/*************************************************/

void solve(void)

{

    int i;

    scanf("%d%d%d", &n, &b, &d);

    sol[1] = 0, set(0);

    search(0, 1);

    for (i = 1; i <= n; ++i)

    {

        if (i%10 != 1) putchar(' ');

        printf("%d", sol[i]);

        if (i<n && i%10 == 0) putchar('\n');

    }

    putchar('\n');

}



int main()

{

    freopen("hamming.in", "r", stdin);

    freopen("hamming.out", "w", stdout);

    

    solve();

    

    fclose(stdin);

    fclose(stdout);

    

    return 0;

}